1. Field of the Invention
This invention relates to a measurement system, particularly to a system for measuring contact image sensor chip shift.
2. Description of the Invention
In a typical image scanning device, such as an image scanner, the following three components are frequently used to capture the image of a subject document: a light source for illuminating a document, an image sensor, and an optical system for focusing document images onto an image sensor. A conventional image sensor array is formed with a charge-coupled device (CCD).
However, in an image scanner scanning an A4 (210 mm wide) document, the lenses system needs to- reduce the A4 document to the extent the CCD is capable of receiving. Consequently, the required optical distance of the lenses system is approximately 300 mm. Hence, the image scanner is bulky. Further, the quality tends to be affected by temperature change and mechanical stress if reflective lenses are used to downsize the device.
Therefore, a contact image sensor (CIS) has been used to replace the aforementioned image sensor of the CCD device (The structure and function of this contact image sensor is described in U.S. Pat. No. 5,724,094). Since the width of the contact image sensor is arranged to be the same as that of an A4 document, image data can be acquired with optical lenses of the same power to plot the document onto the contact image, sensor. As a result, the construction is simplified, and the size of the scanning device is greatly reduced.
As shown in FIG. 1, in the contact image sensor module 20, image sensor chips 12, 14, 16 are generally arranged in a row on the main board 10. During assembly, the image sensor chips 12, 14, and 16 are measured manually with a microscope to spot any shift, and further fixed and sealed onto a frame 15.
However, when these contact image sensor modules 20 are applied to a scanner, any misalignment of the image sensor chips 12, 14, and 16 sealed with the main board onto the frame 1o results n a discontinuity in the scanned image. The only solution after assembly of the scanner is to dismount the frame 15 to inspect the image sensor chips with a microscope. However, the contact image sensor modules can be damaged and become unusable during this destructive ingression.
Accordingly, an object of this invention is to solve the aforementioned problems by providing a system of measuring image sensor chip shift, wherein the gap or pitch of various image sensor chips can be measured with image processing. Thus, even when contact image sensor modules are sealed and fixed, the shift amount of the gaps between various image sensor chips can still be precisely measured without damaging them.
To achieve the above object, this invention provides a method of measuring sensor chip shift comprising the following steps. First, provide a contact image sensor module comprising a plurality of sensor chips arranged in a row on a main board, with each sensor chip having multiple sensors. Next, provide a test chart with a predetermined pattern. Further, enable the multiple sensors of the contact image sensor module to scan the predetermined pattern of the test chart. Moreover, select signal waves sensed by the sensors at the ends of two adjacent sensor chips. Finally, calculate the gap between the sensors at the ends of the two adjacent sensor chips according to the signal waves.
The predetermined pattern of the test chart comprises spaced black and white lines, wherein the spaced black and white lines can be horizontal lines or diagonal lines, and the width of the black and white lines can be the same or different.
When black lines are scanned, their corresponding signal waves indicate a low-luminance area. When these white lines are scanned, their corresponding signal waves indicate a high-luminance area; and when an area composed partially of black lines and white lines are scanned, the luminance of their corresponding signal waves is between that of the high-luminance area and the low-luminance area.
Another method of calculating the gap between the ends of two adjacent sensor chips is to shift horizontally the signal waves corresponding to the sensors between two ends of the adjacent sensor chips until they overlap, and calculate the shifting distance so the horizontal or the vertical gap of the sensors between ends of two adjacent sensor chips can be obtained.
The following describes an embodiment of this invention.